Stromal KITL/SCF promotes pancreas tissue homeostasis and restrains tumor progression.

Components of normal tissue architecture serve as barriers to tumor progression. Inflammatory and wound-healing programs are requisite features of solid tumorigenesis, wherein alterations to immune and non-immune stromal elements enable loss of homeostasis during tumor evolution. The precise mechanisms by which normal stromal cell states limit tissue plasticity and tumorigenesis, and which are lost during tumor progression, remain largely unknown. Here we show that healthy pancreatic mesenchyme expresses the paracrine signaling molecule KITL, also known as stem cell factor, and identify loss of stromal KITL during tumorigenesis as tumor-promoting. Genetic inhibition of mesenchymal KITL in the contexts of homeostasis, injury, and cancer together indicate a role for KITL signaling in maintenance of pancreas tissue architecture, such that loss of the stromal KITL pool increased tumor growth and reduced survival of tumor-bearing mice. Together, these findings implicate loss of mesenchymal KITL as a mechanism for establishing a tumor-permissive microenvironment. Overall design: To assess the functional signifance of cell instrinsic KITL in panreatic mesenchymal cells, we generated Kitl knockdown and overexpression mouse pancretic stellate cell lines (mPSCs) using shRNA. We then performed gene expression profiling analysis using RNA-seq data obtained from all 4 samples with controls included (shCtrl, shKitl, Egfp OE, and Kitl OE).